Semiconductor display device

Abstract

In the case where a still image is displayed on a pixel portion having a pixel, for example, a driver circuit for controlling writing of an image signal having image data to the pixel portion stops by stopping supply of power supply voltage to the driver circuit, and writing of an image signal to the pixel portion is stopped. After the driver circuit stops, supply of power supply voltage to a panel controller for controlling the operation of the driver circuit and an image memory for storing the image data is stopped, and supply of power supply voltage to a CPU for collectively controlling the operation of the panel controller, the image memory, and a power supply controller for controlling supply of power supply voltage to a variety of circuits in a semiconductor display device is stopped.

The invention claimed is: 
     
       1. A semiconductor device comprising:
 a pixel portion comprising a display element and a first transistor; 
 a driver circuit; and 
 a controller comprising a first memory circuit and a second memory circuit comprising a second transistor and a first capacitor, 
 wherein one of a source terminal and a drain terminal of the second transistor is electrically connected to an output terminal of the first memory circuit, 
 wherein the other of the source terminal and the drain terminal of the second transistor is electrically connected to one electrode of the first capacitor, 
 wherein the pixel portion is configured to display a still image after the driver circuit stops supplying an image signal to the pixel portion, 
 wherein the second memory circuit is configured to store data stored in the first memory circuit before the controller stops, and 
 wherein each of the first transistor and the second transistor comprises a semiconductor whose bandgap is wider than bandgap of silicon in a channel formation region. 
 
     
     
       2. The semiconductor device according to  claim 1 , wherein the semiconductor is an oxide semiconductor. 
     
     
       3. The semiconductor device according to  claim 2 , wherein the oxide semiconductor comprises at least one of In, Ga, and Zn. 
     
     
       4. A semiconductor device comprising:
 a pixel portion comprising a display element and a first transistor; 
 a driver circuit; and 
 a controller comprising a first memory circuit and a second memory circuit comprising a second transistor and a first capacitor, 
 wherein one of a source terminal and a drain terminal of the second transistor is electrically connected to an output terminal of the first memory circuit, 
 wherein the other of the source terminal and the drain terminal of the second transistor is electrically connected to one electrode of the first capacitor, 
 wherein the pixel portion is configured to display a still image after the driver circuit stops supplying an image signal to the pixel portion, 
 wherein the second memory circuit is configured to store data stored in the first memory circuit before the controller stops, 
 wherein the second memory circuit is configured to retain the data while the controller stops, respectively, and 
 wherein each of the first transistor and the second transistor comprises a semiconductor whose bandgap is wider than bandgap of silicon in a channel formation region. 
 
     
     
       5. The semiconductor device according to  claim 4 , wherein the semiconductor is an oxide semiconductor. 
     
     
       6. The semiconductor device according to  claim 5 , wherein the oxide semiconductor comprises at least one of In, Ga, and Zn. 
     
     
       7. A semiconductor device comprising:
 a pixel portion comprising a display element and a first transistor; 
 a driver circuit; and 
 a controller comprising a first memory circuit and a second memory circuit comprising a second transistor and a first capacitor, 
 wherein one of a source terminal and a drain terminal of the second transistor is electrically connected to an output terminal of the first memory circuit, 
 wherein the other of the source terminal and the drain terminal of the second transistor is electrically connected to one electrode of the first capacitor, 
 wherein the pixel portion is configured to display a still image after the driver circuit stops supplying an image signal to the pixel portion, 
 wherein the second memory circuit is configured to store data stored in the first memory circuit before the controller stops, and to recover the data to the first memory circuit after the controller restarts, and 
 wherein each of the first transistor and the second transistor comprises a semiconductor whose bandgap is wider than bandgap of silicon in a channel formation region. 
 
     
     
       8. The semiconductor device according to  claim 7 , wherein the semiconductor is an oxide semiconductor. 
     
     
       9. The semiconductor device according to  claim 8 , wherein the oxide semiconductor comprises at least one of In, Ga, and Zn.